The switch power supply uses the switch signals to control the turn-on and turn-off of the switching transistors, and maintains the stable output of the power circuit through the charging and discharging of the energy storage element. In the switch power supply, the control circuit generates switch signals to control the turn-on and turn-off of the switching transistors. The ratio of the on time of the switching transistor to the whole switching period is called duty period. There is a specific relationship between and among the input voltage, the output voltage and the duty ratio of the switch power supply. Therefore, the stable output voltage can be obtained by the feedback adjustment of the duty period when the input voltage fluctuates, and the voltage regulation range of the switch power supply is limited by the range of the duty range.
The constant time control method of switch power supply includes constant on time control and constant off time control. Wherein, the constant on time control method achieves the conversion of the input voltage to an output voltage to drive the load by controlling the turn on of the switch power supply switching transistor at a constant time; the constant off time control method achieves the conversion of the input voltage to an output voltage to drive the load by controlling the turn off of the switch power supply switching transistor at a constant time. Generally, the operational amplifier, comparator and driver module of the control circuit need a certain time to detect and operate, so the off time of the switch signal should be greater than or equal to the minimum off time, and the on time of the switch signal should be greater than or equal to the minimum on time.
The maximum value of the duty period is limited in the constant on time control due to the minimum off time, and the minimum value of the duty period is limited in the constant off time control due to the minimum on time. So, the range of the input voltage and the output voltage of the switch power supply is limited.
Therefore, an expanded range of the input voltage and the output voltage is expected to be further realized.